In recent times, various wireless communication systems use an amplifier system such as Doherty RF power amplifier in the base stations and mobile devices such as mobile phones due to their power efficiency. In many applications, it is highly desirable to reduce the cost, size and weight of the amplifier used in these communication systems. Doherty RF power amplifiers are increasingly being used due to their high-performance, reliability, and cost effectiveness. Doherty RF power amplifier systems amplify signals at high efficiency, with reduced distortion. A typical Doherty RF power amplifier system comprises a main amplifier and a peaking amplifier with an input of the main amplifier coupled to an input of the peaking amplifier by a quarter-wave transmission line. An output of the main amplifier is coupled to an output of the peaking amplifier by a second quarter-wave transmission line. A quarter-wave transmission line is coupled between the output of the peaking amplifier and a device output.
At low amplitude inputs, only the main amplifier is operational. At higher amplitude inputs, the peaking amplifier becomes operational and the quarter-wave delay in the input to the peaking amplifier matches the quarter-wave delay in the output of the main amplifier to the output of the peaking amplifier. Thus, the output of the peaking amplifier is in phase with the output of the main amplifier. In typical Doherty RF power amplifiers, the output matching network including the output matching, combining and output power sampling components constitute a notable portion of the cost, size and weight budgets of the amplifier system.
In view of the foregoing, an improved configuration of the output matching network is desired that results in substantial reduction of the size, weight and cost of the amplifier system.